The present invention relates to an uniaxial eccentric screw pump for transferring a variety of powder substances such as flour, cement, or pigment.
Uniaxial eccentric screw pumps have been used in the past for transferring liquids. Such screw pumps are of two general types, a horizontal type which is used in a horizontal orientation and a vertical type which, of course, is used in a vertical orientation. The basic configuration of both types is, for example, as described in Japanese Provisional Publication No. SHO-60-142078 and Japanese Provisional Publication No. SHO-62-29781, such that a rotor having the shape of a spiral male thread with a circular cross section is mounted in a stator having the shape of a spiral female thread which forms a cavity with an oval cross section. The rotor is rotated around an eccentric center line by means of a connecting rod connected to a drive shaft of a driving unit. A material to be pumped or transferred is sucked into the stator under the influence of the pumping effect produced by the rotor with the circular cross section rotating in the cavity with the oval cross section. The material moves along the major axis of the oval section of the cavity, and the material is discharged from one end of the stator.
Uniaxial eccentric screw pumps of the foregoing types are, as mentioned above, in use mainly for transferring liquid and are said not to be fit to transfer a powder. Only the type of pump of FIG. 3 was available as an uniaxial eccentric screw pump for transfer of powder material. A prior art pump for powder transfer is, as shown in FIG. 3 of the drawings, of the horizontal type. A powder feed inlet (e) (formed by a hopper) is formed in a pump casing (a) adjacent a suction chamber (k) which is close to the coupling between a rotor (c) and a connecting rod (d). Powder is charged into the suction chamber (k) through the powder feed inlet (e), and the powder is then passed through a cavity in a stator (b) and discharged out of a powder discharge port (f) and a discharge nozzle (j). Jet ports (g) and (h) for compressed air jets are provided in the bottom of the suction chamber (k) and near the powder discharge port (f), respectively, producing air streams which assist the transfer of powder. Accordingly, powder which is fed through the powder feed port (e) is fluidized by the air supplied from the jet port (g) of compressed air, and the powder is transferred out of the discharge nozzle (j) under the influence of the flow of compressed air jetted out of the compressed air jet port (h).
One popular conventional method for transferring powder is the so-called pneumatic conveying in which compressed air is blown into a powder transfer tube by a blower or the like, and powder contained in a hopper or the like is fed into the transfer tube at a constant rate by means of a feeder, to be transported by the air stream to a desired destination.
There are, however, problems with the foregoing prior art structures. To operate the above-mentioned conventional uniaxial eccentric screw pump for powder transfer, it is necessary to feed powder into the feed inlet (e) in advance of the start of powder transfer. It, therefore, is not possible to directly suck in powder contained in a vessel such as a drum by means of the pump so as to transfer it to a desired place. Further, jetting of compressed air out of the jet port (g) of the suction chamber (k) is indispensable. If air is not jetted out of the jet port (g), powder fed into the feed inlet (e) may form a bridge and prevent powder from being sucked into the cavity of the stator (b).
In the case of transferring powder by the above-mentioned pneumatic conveying, it is necessary to separate the air by means of a bag filter, etc. after the transfer since the powder is transferred with a volume of air which is several times as large as that of powder. Hence the blower or the like must have a very large capacity, resulting in a large-sized apparatus. Furthermore, as is the case of the conventional screw pump, powder should be charged in advance in the hopper or the like.
The present invention has the purpose to solve the above-mentioned problems of the conventional apparatus. In particular, it provides a vertical type uniaxial eccentric screw pump which is capable of, without jetting compressed air inside the pump, directly sucking in powder contained in a vessel through a suction port provided in the lower end of the pump and transferring the powder to a desired place.